No. 118 

1961 

EFFECT OF DIELDRIN IN THE GLUE LINE OF OAK PLYWOOD 

PANELS IN PREVENTING LYCTUS BEETLF: DAMAGE 

For many years the lumber industry has been seeking 

improved methods of preventing decay and insect damage to 

lumber and other wood products. One relatively new approach 

to this problem is the addition of toxic chemicals ih plywood glues to prevent infestations or restrict feeding injury by wood-boring insects. Wood products treated in this 

manner have been marketed in some countries, and studies 

have shown that the toxic additives are effective in preventing certain types of insect damage .' 

At present, similarly treated plywood is not available in the United States. However, test samples have been 

prepared by manufacturers interested in a damage-free product. In 1958, special oak plywood panels were made for testing the effectiveness of various concentrations of dieldrin2 

in several types of glue for preventing infestations by a 

powder post beetle. This note summarizes the initial results with this experimental product. 

l~amblyn, N. and Gordon, A. Control of borer attack in plywood by use of 

preservative in the glue. CSIRO Forest Prod. News Let. 180: 1-2. 1950. 

hntion of canmercial products is not to be construed as endorsement of 

them by the Forest Service or U. S. Department of Agriculture. 
Test Materials 

Plywood.--The test samples were red oak plywood (3/16 

inch-3 ply) panels, 6 inches square, with dieldrin combined 

in four adhesive mixes. Dieldrin concentrations were based 

on percent of weight of glue solids and varied from 0.1 to 

0.5 percent. The panels were coded as follows: 

Dieldrin Content -- 

Code Percent Actual 

Adhesive mix - No. A B C D 

Cold Press Casein K 8881 0.0 0.1 0.25 0.5 

Cold Press Urea K 8882 .o .1 .25 .5 

Hot Press Urea K 8883 .O .1 .25 $5 

Hot Press Phenol K 8884 .O .1 .25 .5 

Each test replicate included the 16 possible combinations of 

glue-dieldrin mixtures. Fresh-cut pieces of oak limbwood of 

the type used to breed Lyctus were added to each replicate 

as controls to help evaluate the test method and the suitability of the plywood as food for the beetles. 

Insects.--Adults of the southern lyctus beetle, 

Lyctus planicol lis Lec., were the test insects, and only 

those beetles which had emerged within a 24-hour period from 

infested wood in culture cans were used as test specimens. 

Procedure 

Each 6-inch plywood panel was quartered into 3-inch 

squares, and two of these were designated as samples for 

each panel. The exposed toxic glue line was sealed with 

paraffin. Test containers were glass lantern chimneys with 

cheesecloth covers. Thirty Lyctus adults were placed in 

each container with two plywood sections. 

Five replicates were exposed to attack in November 

and December 1958 and maintained at room temperature (72' - 75OF.) and low humidity. Two more replicates were started 

in March 1959 in a temperature-humidity controlled room at 

80°F. and approximately 40-percent humidity. These latter 

conditions are very favorable for powder post beetle development. In the first lot when no evidence of Lyctus feeding 

was detected in 5 months (where the humidity possibly was 

too low for normal development), the test samples of these 

five replicates were transferred to the controlled room in 

May and reinfested with fresh beetles. 

At the conclusion of the test in December 1959, each 

plywood section was examined microscopically and partially 

dissected whenever suitable oviposition sites for the beetle 

were evident. Where larval frass or an opening to the sur- 
Table 1.--Summary of data on plywood sections 

attacked bv beetle larvae 

Dieldrin Test 

concentration units Infested Potential damaging insects 

1 

Percent Number Percent Number Percent 

0.0 10 41.7 135 81.8 

.1 10 41.7 2 3 13.9 

-25 3 12.5 6 3.7 

.50 1 4.1 1 .6 

i 

'~hese are insects removed by dissection of the plywood. 

face was detected, the galleries were exposed to measure 

the length and depth of penetration by the larvae. On the 

oak limbwood controls, only adult emergence holes were 

counted, indicating the successful completion of a generation. 

Results 

There was no obvious damage to any of the plywood 

sections. However, microscopic examination revealed that 

eggs were deposited and hatched on 21 percent of the test 

panels. Table 1 summarizes the data on the infested plywood 

sections. 

All the Lyctus beetle larvae recovered in dissection 

were dead, and feeding had been restricted to 2/16 to 3/16 

of an inch laterally and about 1/32 of an inch in depth. No 

direct tunneling to the toxic glue line was apparent, although there is the possibility that toxic chemical penetration from the glue could have influenced survival. Since 

feeding patterns did not vary between toxic and nontoxic 

test samples, it was concluded that the larvae survived for 

only a brief period and that a deficiency of necessary nutrients was the primary control factor. Other recent studies 

have shown that the nutritional requirements of Lyctus are 

quite exacting, with high starch content a critical component of the larval diet. Apparently the plywood used in 

this test was largely heartwood and low-starch sapwood which 

is unsuitable for normal development and survival. 

In contrast, nearly all the 1 x 3-inch cylindrical 

sections of oak limbwood were moderately to heavily infested. 

Larvae were still actively feeding when the test was terminated. Five sets of these controls completely disintegrated 
in 4 to 5 months from heavier attack, and in all cases, an 

accurate count of the numbers of emerging adults was impossible. 

In summary, no significant effect was shown by different concentrations of dieldrin in the glue line of the 

test plywood sections. The type of glue apparently did not 

affect the results. Because starch content is a critical 

factor, it is suggested that further testing of this potentially valuable method of preventing Lyctus beetle damage to 

oak plywood be done using woods with high-starch content. 

Or, so long as low-starch content material is used, the plywood is relatively safe from attack. 

--THOMAS McI NTYRE 

Forest Entomologist 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture 

Laurel, Md.